This invention relates to a socket having contact elements which in connection with mounting and removal of an IC package (electrical part and/or semiconducting integrated circuit), an electrical connection is made with this IC package.
Typically, at a semiconductor manufacturing plant, before shipping IC packages, in which semiconductor integrated circuit chips are resin-sealed, they are put through a reliability test which is called burn-in, in order to discriminate between good and defective units. Burn-in consists of operating the IC packages, which have passed functional tests for a certain amount of time at a high temperature of 120.degree. C. and at a source voltage which is higher than the rated value by about 20%. The IC packages which have operation failures during burn-in are discarded as defective units, and the IC packages which continue operating normally are shipped out as good items.
The construction of a conventional prior art socket which has been used for mounting IC packages during such burn-in is shown in FIGS. 13-16. FIGS. 13 and 14 are a plan view, and a side view, respectively, of the conventional socket, and FIGS. 15 and 16 are enlarged partial cross-sectional views of this conventional socket.
As shown in FIG. 14, this socket is made up of a base 100, serving as the socket main body, which is affixed to a printed-circuit board (not shown in the figure ), and a cover 102 which is provided so that it can reciprocate in relation to base 100. A square-shaped opening 106 is provided in cover 102 for plugging on IC package 104 in and out of the socket as shown in FIG. 13. When the cover 102 moves in the vertical direction in relation to the base 100, the corner sections 106a at the four corners of this opening 106 are guided by two exterior surfaces 108a of four guides 108, respectively, which are positioned on the base 100.
The top surface of the base 100 is constructed so that a QFP (Quad in line Flat Package) type IC package 104 can be mounted. The respective two interior surfaces 108b of each of the guides 108 are slanted and cone-shaped grooves 108c, which somewhat widen relative to a direction taken towards the base, are formed in their corner sections. The corner sections of the IC package 104 are guided by means of these groove 108c. Also, L-shaped ribs 110 are provided on the base 100, coming close to the base ends of the grooves 108c. The IC package 104 is positioned on the top surface of the base by means of these ribs 110. Multiple contacts 112, which correspond to the row of lead terminals on each side of the IC package 104, are provided in a row on the base 100, between two adjacent guides 108.
With reference to FIGS. 15 and 16, contacts 112 can be made by punching thin plates, for example, of beryllium bronze and such. There is a base end section 112a which is embedded in the base 100, a circular spring section 112b which extends from the upper end section of this base end section 112a in a curved (generally semi-circular) manner, a lever section 112c which extends in a straight line from the upper edge of this circular spring section 112b upward, a lead presser 112d which extends almost horizontally in the direction toward the central section of the socket (the IC package mounting section) from the upper edge of the circular spring section 112b, and a hook-shaped contact section 112e which is formed on the front end of this lead presser 112d. Socket terminal pins 112f protrude straight down from the lower edge of the base end section 112a.
The front end 112g of the lever section 112c normally is in contact with and abuts the slanted sliding contact surface 114a of the cam section 114 which protrudes from the bottom surface the cover 102. When the cover 102 moves downward as shown in FIG. 15 in relation to the base 100, the front end 112g of the lever section 112c follows the slanted sliding contact surface 114a of the cam section 114, thereby causing the lever section 112c to displace towards the outside of the socket. A dividing wall 114b is provided on the slanted sliding contact surface 114a for guiding both sides of lever section 112 and for preventing contact with the adjacent contact 112 .
The operation of each section of contacts 112 during the mounting of an IC package 104 in this socket is set forth below.
First, in the state wherein the IC package 104 is not mounted, the cover 102 is moved by pressing it onto the base 100. By this means, the cam section 114 of the cover 102 moves downward, whereas the lever section 112c, which is in sliding contact with the slanted sliding contact surface 114a is displaced outward from the center of the socket. The circular spring section 112b is displaced in the same direction as the lever section 112c with its arc being slightly contracted. That is, the upper edge of the circular spring section 112b and the bottom edge of lever section 112c sag slightly. Correspondingly, the contact section 112e on the front end of the lead presser 112d is displaced toward the outside of the socket while rising upward. In this state, wherein the contact sections 112e of the contacts 112 are withdrawn diagonally upward from a lead holding surface 116, the IC package 104 can be passed through the opening 106 from above the cover 102 and mounted into this socket. The IC package 104 is guided to the base 100 by the grooves 108c of the interior corner sections of the guides 108 and is positioned on the base 100 by the ribs 110. By this means, the front end bent sections of the leads 104a of the IC package 104 are placed in designated positions on the lead holding surface 116 on the base 100. The state wherein the IC package 104 is installed in this socket in this manner is shown in FIG. 16.
Next, the cover 102 is released so that it is not pressed down against the base. When this is done, owing to the resilient biased force of the circular spring sections 112b of the contacts 112, the cover 102 rises to the original position. The contacts 112 then almost recover their original shape, with the front end contact sections 112e of the lead pressers 112d pressing down on the front end bent section of the lead 104a of the IC package 104. By this means, the recovery of the contact 112 is restricted only by the thickness of the lead 104a with the lead presser 112d slightly bowed, and by means of the elastic force of this lead presser 112d and the circular spring section 112b, the front end contact section 112e is pressed into engagement with the front end bent section of the lead 104a. In FIG. 15, the state is shown wherein an electrical connection is established between the IC package 104 and the socket. The dividing wall 118 is positioned on the lead holding surface 116 of the base 100 so that the contact sections 112e of the contacts 112 do not come into contact with those of the adjacent contacts 112.
In order to remove the IC package 104 from this socket, the cover is again depressed toward base 100 with the front end contact sections 112e of the contacts 112 being withdrawn from the leads 104a of the IC package 104. The IC package 104 then can be removed by means of a pair of tweezers or the like.
The above-mentioned prior art socket accomplishes the installation and removal of IC packages 104 from these sockets by displacing the contacts 112 using a reciprocating cam mechanism made up of the cam section 114 of the cover 102 and the lever section 112c of the contact 112. In this conventional socket the force of pushing down the cover 102 (the operating force) necessary for displacing the contacts 112 from the position in FIG. 15 to the position in FIG. 16, is determined by the elastic force of the lever sections 112c based on the circular spring sections 112b of the contacts 112, the angle of inclination of the cam section 114 of the cover 102, and the angle of friction of the slanted sliding contact surface 114a of the cam section 114 with the front end of the lever 112g. For example, in the case wherein the elastic force of the lever section 112c is 30 gf, the angle of inclination of the cam section 114 is 60 degrees and the friction angle is 15 degrees, the operating force which is necessary for one contact 112 would be 22 gf.
However, because multiple contacts 112 are provided in sockets of this type which correspond to the leads (pins) of electrical components such as the above-mentioned IC package 104, the operating force which is necessary for all of the contacts 112 becomes a value which is much greater. This operating force is obtained by multiplying the number of all the contacts by the operating force that is necessary for one contact 112. Additionally, as the degree of integration of the IC chips has increased, the number of leads (pins) of IC packages has also increased and the pitch between leads has generally decreased. Therefore, in the sockets of this conventional type, the operating force for the entire socket has become much larger, and its operation has become more difficult, whether it is automatically or manually operated.
To address this problem, diminishing the operating force in these conventional sockets has been tried by means of extending the lever section 112c of the contact 112, reducing the elastic force of the lever section 112, and increasing the angle of the cam section 114 of the cover 102. However, if these actions are pursued, then there is the problem that the amount of cover 102 movement increases, and/or the outer dimensions of the socket are increased. Also, if the lever section 112c of the contact 112 is extended, there is the risk that the contact 112 will become easily bent and will "short out" against adjacent contacts.